Conventionally, a manufacturing process of semiconductor devices has been performed in a so-called clean room where a degree of cleanliness is maintained at a high level. However, as semiconductor wafers (hereinafter, referred to as “wafers”) and various processing apparatuses processing the wafers have become larger, the operating cost of the clean room has been increased. Thus, a technique of maintaining the degree of cleanliness inside a processing apparatus and inside a substrate storage container which is called a front-opening unified pod (FOUP) used in delivery of wafers between processing apparatuses at a high level has been recently adopted.
The above-mentioned substrate storage container is configured to store a plurality of wafers in multi-tiers in parallel to each other, and carry the wafers into/out of an opening formed on a surface of the substrate storage container. Nitrogen gas having a high degree of cleanliness is enclosed in the substrate storage container to prevent entrance of contaminants such as particles into the substrate storage container.
However, in addition to unprocessed wafers, wafers which have been processed in a processing apparatus are also stored in the substrate storage container. Therefore, particles adhered to the wafers in the processing apparatus may be brought into the substrate storage container. Then, other wafers may be contaminated by the particles, and thus, the product yield may be decreased.
As a method for removing particles adhered to wafers, for example, Patent Document 1 suggests a technique of injecting a purge gas having a high degree of cleanliness onto each surface of wafers stored in multi-tiers in a substrate storage container.